bnxt: HW_LRO Rx Pkt with > 32 fragments caused Crash (iflib)

Broadcom NIC with HW_LRO setting max_agg_segs >= 6 can generate Rx pkt with
64 (2^6) fragments, modify IFLIB_MAX_RX_SEGS to 64 to avoid memory
corruption / Crash.

Submitted by: Bhargava Chenna Marreddy <bhargava.marreddy@broadcom.com>
Reviewed by: shurd, sbruno
Approved by: sbruno (mentor)
Sponsored by: Broadcom Limited
Differential Revision: https://reviews.freebsd.org/D12774